P-modified epoxy resin, phenolic OH compound and polyamine

ABSTRACT

Epoxy resin mixtures for prepregs and composites 
     Epoxy resin mixtures for preparing prepregs and composites contain the following components: 
     a phosphorus-modified epoxy resin with an epoxy value of 0.02 to 1 mol/100 g, made up of structural units derived from 
     (a) polyepoxy compounds with at least two epoxy groups per molecule and 
     (b) phosphinic acid anhydrides, phosphonic acid anhydrides, or phosphonic acid half-esters; 
     a glycidyl group-free compound with phenolic OH groups in the form of bisphenol-A, bisphenol-F, or a high-molecular phenoxy resin obtained through the condensation of bisphenol-A or bisphenol-F with epichlorohydrin; 
     an aromatic polyamine used as a hardening agent.

BACKGROUND OF THE INVENTION

The invention concerns epoxy resin mixtures for the production ofprepregs and composites, as well as the prepregs and composites producedfrom these epoxy resin mixtures.

Composites based on epoxy resins and inorganic or organic reinforcingmaterials have become very important in many industrial fields and ineveryday life. The reasons therefor are, on the one hand, the relativelysimple and safe processing of epoxy resins and, on the other hand, thegood mechanical and chemical properties of cured epoxy resin moldedmaterials, which allow adaptation to different applications andadvantageous utilization of the properties of all the materials whichare part of the composite.

Epoxy resins are advantageously processed into composites viapreparation of prepregs. For this purpose inorganic or organicreinforcing materials or embedding components in the form of fibers,non-woven and woven fabrics, or of flat shaped articles are impregnatedwith the resin. In most cases this is accomplished with a solution ofthe resin in an easy-to-evaporate or easy-to-volatilize solvent. Theprepregs thus obtained must no longer be tacky, but must not yet behardened after this process, but rather the resin matrix must be in apre-polymerized state. In addition, the prepregs must have sufficientlylong shelf life. Thus, for example, a shelf life of at least threemonths is required for circuit board manufacturing. When they arefurther processed into composites, prepregs must also melt on when thetemperature is increased and must bond with the reinforcing materials orembedding components as well as with the materials provided for thecomposite as firmly and permanently as possible under pressure, i.e.,the crosslinked epoxy resin matrix must have a high interfacial adhesionto the reinforcing materials, or embedding components, as well as to thematerials to be bonded such as metals, ceramics, minerals, and organicmaterials.

In the cured state, composites are normally expected to have highmechanical strength and thermal stability, as well as chemicalresistance, and heat distortion or resistance to aging. Forelectrotechnical and electronic applications, the requirements alsoinclude permanently high electrical insulation capability and, forspecial applications, a plurality of other requirements. For use ascircuit board material, for example, high dimensional stability over abroad temperature range, good adhesion to glass and copper, high surfaceresistivity, low dielectric loss factor, good machinability(punchability, drillability), low water absorption, and high corrosionresistance are required.

With increasing load and intensive use of the composites, in particularthe requirement for heat distortion becomes especially important. Thismeans that the materials must resist high temperatures withoutdeformation or damage of the composite, for example by delamination,during processing and use. Circuit boards, for example, are exposed totemperatures of over 270° C. during flow soldering. Temperatures over200° C. may also occur temporarily and in a limited area during cuttingand drilling. Materials with a high glass transition temperature haveadvantageous characteristics in this respect. If the glass transitiontemperature is above the aforementioned values, dimensional stability inthe temperature range prevailing during processing is generally ensuredand damage such as warping and delamination are mostly avoided. Theepoxy resin currently used worldwide for FR4 laminates has a glasstransition temperature T_(g) of only 130° C. after curing. This results,however, in the above-mentioned type of damage and failure duringmanufacturing. Therefore it has for long been desired to havecomparatively easy-to-process and inexpensive materials with a glasstransition temperature T_(g) of over approx. 180° C.

Another requirement that is becoming more and more important is that offlame resistance. In many areas this requirement has first priority dueto possible hazards to people and property, for example, in constructionmaterials for aircraft and automobile manufacturing, as well as forvehicles in public transportation. Flame resistance of circuit boardmaterials is essential in electrotechnical, but especially electronic,applications due to the high value of the electronic components mountedon the boards.

Therefore materials must pass one of the strictest tests and attain V-0classification by UL 94 V, for evaluating their flammability. In thistest, a test object is exposed to a well-defined flame positionedvertically under its lower edge. The sum of burning times in ten testsmay not exceed 50 s. This requirement is difficult to meet, especiallyif the material is thin, as is the case in electronics. The epoxy resinindustrially used worldwide for FR4 laminates only meets theserequirements because it contains approximately 30% to 40%ring-brominated aromatic epoxy components, with reference to the resin,i.e., approximately 17%-21% bromine. For other applications, comparablyhigh concentrations of halogen compounds are used, often also combinedwith antimony trioxide as a synergist. The problem with these compoundsis that, while they are highly effective as fireproofing agents, theyalso have very objectionable properties. Thus, antimony trioxide islisted as a carcinogenic chemical, and aromatic bromine compounds,during thermal decomposition, not only split off bromine radicals andhydrogen bromide, which are highly corrosive, but, especially the highlybrominated aromatic compounds may also form highly toxic polybrominebenzofurans and polybromine benzodioxins upon decomposition in thepresence of oxygen. The disposal of bromine-containing waste materialsand toxic waste represents another problem.

Materials that partially or fully meet the heat distortion requirementinclude, for example, bismaleinimide/triazine (BT) -based moldedmaterials with a T_(G), of approximately 200° C. or polyimide (PI) witha T_(G) of260° to270° C. Recently also BT/epoxy blends with a T_(G) of180° C.,as well as cyanate ester resins with a T_(G) >200° C., have alsobecome available. Laminates manufactured with these resin systemsexhibit, however, poorer processing and machining characteristicscompared to epoxy resin-based laminates. Thus, for example, theproduction of PI-based laminates requires press temperatures ofapproximately 230° C. and considerably longer after-curing times(approx. 8 h) at temperatures of 230° C. Another disadvantage of theseresin systems is their six to ten times higher material costs.

A comparatively inexpensive resin system is obtained if aromatic and/orheterocyclic polyepoxy resins, i.e., polyglycidyl compounds, arecombined with aromatic polyamines acting as hardening agents. Suchpolyamines known, for example, from German Patent 2,743,680, result innetwork polymers that exhibit a particularly high heat distortion andresistance to aging. European Patent 274,646 discloses that, using 1,3,5-tris (3-amino-4-alkylphenyl)-2,4,6-trioxohexahydrotriazines ashardening agents, laminates with a glass transition temperature of up to245° C. and good processing and machining characteristics can beobtained.

Although the above-mentioned resin systems have a widely differentflammability, they all share the disadvantage of being insufficientlyflame-retardant. Therefore, in order to meet the requirement of passingthe UL 94 V combustibility test with a V-0 classification, which isessential for many applications, the use of highly effectivebromine-containing fireproofing agents cannot be avoided. As a result,both the potential hazard associated with bromine compounds and theimpaired thermal-mechanical characteristics caused by the brominecompounds must be taken into account.

For these reasons, extensive research has been conducted to replacebromine-containing fireproofing agents with less problematicalsubstances. Thus, for example, fillers (with extinguishing gas effectssuch as aluminum oxide hydrates (see J. Fire and Flammability, Vol. 3(1972), pp. 51 ff.), basic aluminum carbonates (see Plast. Engng., Vol.32 (1976), pp. 41 ff.) and magnesium hydroxides (EuropeanOffenlegungsschrift 243,201, as well as vitrifying fillers such asborates (see Modern Plastics, Vol. 47 (1970), No. 6, pp. 140 ff) andphosphates (U.S. Pat. No. 2,766,139 and U.S. Pat. No. 3,398,019) havebeen proposed. All these fillers have, however, the disadvantage ofworsening, in some cases considerably, the mechanical, chemical, andelectrical properties of the composites. In addition, they requirespecial, more complicated processing methods, since they tend tosedimentation and increase the viscosity of the filled resin system.

The flame-retardant properties of red phosphorus has also been described(U.K. Patent 1,112,139), optionally in combination with finely dispersedsilicon dioxide or aluminum oxide hydrate (U.S. Pat. No. 3,373,135).According to these documents, materials are obtained whose use inelectrotechnical and electronic applications is limited due to thephosphoric acid produced in the presence of moisture and the associatedcorrosion. Organic phosphorus compounds, such as phosphoric acid esters,phosphonic acid esters, and phosphines, have also been proposed asflame-retardant additives (see W. C. Kuryla and A. J. Papa FlameRetardance of Polymeric Materials, Vol. 1, Marcel Dekker Inc., New York,1973, pp. 24-38 and 52-61). Since these compounds are known for their"softening" characteristics and are therefore extensively used worldwideas plasticizers for polymers (U.K. Patent 10,794), this alternative istherefore also not very promising.

In order to achieve flame-resistance according to UL 94 V-0, GermanOffenlegungsschrift 3,836,409 discloses a method for preparing prepregsby impregnating certain reinforcing materials or flat shaped articleswith a suspension of halogen-free, nitrogen- and phosphorus-containingfireproofing agents in a solution of aromatic, heterocyclic, and/orcycloaliphatic epoxy resins (in a non-ring-halogenated form or aring-halogenated form with low halogen content) and aromatic polyaminesand/or aliphatic amines acting as hardening agents. The fireproofingagents are halogen-free melamine resins or organic phosphoric acidesters, particularly melamine cyanurates, melamine phosphates, triphenylphosphate, and diphenylcresyl phosphate, as well as their mixtures.This, however, is also not a very promising solution, since the fillersused always increase water absorption, and therefore prevent thematerial from passing the circuit board-specific tests.

Organic phosphorus compounds, such as epoxy group-containing phosphoruscompounds, which can be anchored in the epoxy resin network, can also beused for providing epoxy resins with flame-retarding characteristics.Thus, European Patent 384,940 discloses epoxy resin mixtures containinga commercially available epoxy resin, the aromatic polyamine1,3,5-tris(3-amino-4-alkylphenyl)-2,4,6-trioxo-hexahydrotri azine and anepoxy group-containing, glycidyl phosphate-, glycidyl phosphonate- orglycidyl phosphinate-based phosphorus compound. With such epoxy resinmixtures, flame-retardant laminates or composites that meet the V-0classification requirements of UL 94 and have a glass transitiontemperature >200° C., can be obtained without adding halogens.Furthermore, these epoxy resin mixtures can be processed in a mannersimilar to that used for currently used epoxy resins.

Circuit boards constitute the basis for the production of electronicassemblies. They are used for connecting a variety of electronic andmicroelectronic components with one another to form electronic circuits.The components are connected to the circuit board by gluing or solderingusing complex, highly automated assembly processes. Also in automaticinsertion, there is a trend toward more streamlined manufacturingmethods. Therefore IR reflow soldering, expected to replace othersoldering processes in the future, is increasingly used in SMDtechnology. In this process, the entire circuit board is heated totemperatures >260° C. in a few seconds using IR radiation; thisinstantly evaporates any water absorbed in the circuit board. Onlylaminates with excellent interlaminar adhesion survive IR solderingprocesses without being destroyed by delamination. In order to reducethis hazard, expensive conditioning processes have been proposed (seeGalvanotechnik, Vol. 84 (1993), pp. 3865-3870).

It is known that in laminates with high glass transition temperature,for example, based on PI- or BT-resins, the interlaminar adhesion isweaker than in the halogen-containing FR4 laminates that are beingpredominantly used today; this is also true for the laminates known fromEuropean Patent 384,940. Most of the circuit boards manufactured todayare multilayer (ML) circuit boards, which contain a plurality ofstructured conductor planes spaced and insulated from one another byepoxy resin compounds. The current trend in ML technology, however, istoward an increasing number of structured conductor planes; thus,currently multilayer circuit boards with more than 20 structuredconductor planes are being manufactured. Since excessive overallthickness of these circuit boards must be avoided for technical reasons,the distance between the structured conductor planes is becomingincreasingly smaller and thus interlaminar adhesion and copper adhesionin ML laminates with high glass transition temperature is becoming moreand more problematic. In addition, this type of circuit board must havea high solder bath resistance in the case of IR soldering.

As stated earlier, it is known from European Patent 384,940 thatlaminates with a flame resistance meeting the requirements can beobtained without using halogens through phosphorus modification ofimpregnation resins. It was found, however, during production research,that phosphorus-modified laminates are subject to delamination during IRsoldering. Therefore, urgent need has arisen for electrolaminates havingthe required flame resistance without the use of halogens, for examplethrough incorporating phosphorus into the resin matrix, but which arealso suitable for IR soldering required for SMD technology. Thisrequires electrolaminates with extremely high solder bath resistance. Incircuit board technology, the high-pressure cooker test (HPCT) and thedetermination of solder bath resistance are primarily used to test thesuitability of laminates for high thermal stressing. In HPCT, a laminatespecimen (5×5 cm), freed of copper, is exposed to 120° C. andapproximately 1.4 bar steam pressure for 2 h and then placed to float ona 260° C. hot solder bath. The time to delamination is then measured.Qualitatively good laminates exhibit no delamination up to >20 s. Solderbath resistance is determined on 2×10 cm large laminate specimens bydipping them into a 288° C. hot solder bath and measuring the time todelamination.

SUMMARY OF THE INVENTION

The object of the invention is to provide epoxy resin mixtures that canbe obtained in a simple and therefore inexpensive manner and are easy toprocess compared to epoxy resins currently used in industry, aresuitable for the production of prepregs and laminates for multilayertechnology, can be made into molded materials with as high a glasstransition temperature as possible (≧180° C.) and are highlyflame-retardant, meeting the requirements of UL 94 for V-0classification, without the addition of halogens, and have at the sametime a solder bath resistance that is sufficiently high so that IRsoldering processes can be used for electronic assembly manufacturingwithout delamination.

DETAILED DESCRIPTION OF THE INVENTION

This object is achieved according to the invention through epoxy resinmixtures containing the following components:

a phosphorus-modified epoxy resin with an epoxy value of 0.02 to 1mol/100 g, made up of structural units derived from

(a) polyepoxy compounds with at least two epoxy groups per molecule and

(b) phosphinic acid anhydrides, phosphonic acid anhydrides, orphosphonic acid half-esters;

a glycidyl group-free compound with phenolic OH groups in the form ofbisphenol-A, bisphenol-F, or a high-molecular phenoxy resin obtainedthrough the condensation of bisphenol-A or bisphenol-F withepichlorohydrin;

an aromatic polyamine with the following structure used as a hardeningagent: ##STR1## where one of the radicals R¹ and R² on each aromaticpartial structure denotes a H atom and the other one denotes an alkylgroup.

The phosphorus-modified epoxy resins contained in the epoxy resinmixtures according to the invention are obtained by reactingcommercially available polyepoxy resins (polyglycidyl resins) with thefollowing phosphorus compounds:

phosphinic acid anhydrides: anhydrides of phosphinic acids with alkyl,alkenyl, cycloalkyl, aryl, or aralkyl radicals; these may include:dimethylphosphinic acid anhydride, methylethylphosphinic acid anhydride,diethylphosphinic acid anhydride, dipropylphosphinic acid anhydride,ethylphenylphosphinic acid anhydride, and diphenylphosphinic acidanhydride;

bisphosphinic acid anhydrides: anhydrides of bisphosphinic acids,particularly of alkane-bisphosphinic acids with 1 to 10 carbon atoms inthe alkane group;

examples therefor include: methane-1,1-bis-methylphosphinic acidanhydride, ethane-1,2-bismethylphosphinic acid anhydride,ethane-1-2-bis-phenylphosphinic acid anhydride andbutane-1,4-bis-methylphosphinic acid anhydride;

phosphonic acid anhydrides: anhydrides of phosphonic acids with alkyl,alkenyl, cycloalkyl, aryl, or aralkyl radicals; these may include:methanephosphonic acid anhydride, ethanephosphonic acid anhydride,propanephosphonic acid anhydride, hexanephosphonic acid anhydride, andbenzenephosphonic acid anhydride;

phosphonic acid half-esters: those preferably used include half-esters,i.e., monoesters of phosphonic acids with alkyl radicals (preferablywith 1 to 6 carbon atoms) or with aryl radicals (in particularbenzenephosphonic acid) with aliphatic alcohols, in particularlow-boiling aliphatic alcohols such as methanol and ethanol;

examples include: methanephosphonic acid monomethyl ester,propanephosphonic acid monoethyl ester, and benzenephosphonic acidmonomethyl ester;

phosphonic acid half-esters can be obtained by partial hydrolysis of thecorresponding phosphonic acid diesters, in particular using sodiumhydroxide solution or by partial esterification of free phosphonic acidswith the corresponding alcohol. The preparation of phosphorus-modifiedepoxy resins of the above-mentioned types is also described in theGerman Offenlegungsschriften 4,308,184 and 4,308,185.

In general both aliphatic and aromatic glycidyl compounds, as well astheir mixtures, can be used to obtain phosphorus-modified epoxy resins.Preferably bisphenol-A-diglycidyl ether, bisphenol-F-diglycidyl ether,polyglycidyl ethers of phenol-formaldehyde and cresol-formaldehydenovolaks, diglycidyl esters of phthalic, isophthalic, terephthalic, andtetrahydrophthalic acid, as well as mixtures of these epoxy resins, areused. Other polyepoxides are described in Handbook of Epoxy Resins byHenry Lee and Kris Neville, McGraw-Hill Book Company 1967 and in themonograph by Henry Lee Epoxy Resins, American Chemical Society 1970.

Among the possible phosphorus-modified epoxy resins, phosphonicacid-modified epoxy resins, such as methyl, ethyl, and propylphosphonicacid-modified epoxy resins have been found to be particularlyadvantageous, in particular with a phosphorus content of 2 to 5 wt. %,for the production of solder-bath-resistant electrolaminates.Furthermore, phosphorus-modified epoxy resins with an average of atleast one epoxy function, in particular those with an average of atleast two epoxy functions, have been found advantageous. Suchphosphorus-modified epoxy resins can be prepared by reacting epoxynovolak resins having a functionality of approximately 3 to 4 withphosphonic acid anhydrides. The phosphorus-modified epoxy resins contain0.5 to 13 wt. % phosphorus, preferably 1 to 8 wt. %. The overallphosphorus content of the epoxy resin mixtures, i.e., the impregnationresin mixtures, is 0.5 to 5 wt. %, preferably 1 to 4 wt. %.

The epoxy resin mixtures according to the invention contain a glycidylgroup-free compound with phenolic OH groups. This compound is added toachieve specific characteristics. Bisphenol-A and bisphenol-F, as wellas phenoxy resins serve this purpose. These are linear condensationproducts of bisphenol-A and bisphenol-F with epichlorohydrin in the formof high-molecular compounds with a molecular weight of up to 30,000; theend-position phenolic OH function content is very small, much less than1%. The preparation method and properties of such phenoxy resins areknown (see Encyclopedia of Polymer Science and Engineering (secondedition), Vol. 6, pp. 331 and 332, John Wiley & Sons, Inc., 1986). Thecompound with phenolic OH groups is added in the amount of 0 to 20 wt.%, preferably from 0 to 10 wt. %, to the epoxy resin mixtures accordingto the invention. It must be taken into account that the glycidylgroup-free phenolic component can only be added in a proportion wherethe flame-resistance requirement of UL 94 V specification is still met.

The aromatic polyamines that serve as hardening agents in the epoxyresin mixtures according to the invention are well-known. Polyamineswith the above-mentioned structure with R¹ =alkyl and R² =H aredescribed in European Patent 274,646.

They are prepared by trimerization of 2,4-diisocyanato-alkylbenzenes andsubsequent hydrolysis of the remaining isocyanate groups. Compounds withR¹ =H and R² =alkyl are obtained similarly by trimerization of2,6-diisocyanato-alkylbenzenes and subsequent hydrolysis. Bothpolyamines of the two aforementioned types and mixtures of thesecompounds can be used as hardening agents in the epoxy resin mixturesaccording to the invention. In addition, polyamines obtained bytrimerization of mixtures of 2,4-and 2,6-diisocyanate\0-alkylbenzenesand subsequent hydrolysis of the trimerizate can also be used. Suchmixtures are available in bulk quantities and allow the hardening agentcomponent to be manufactured inexpensively. The hardening agent contentin the resin mixture is advantageously 1 to 45 wt. %, preferably 5 to 30wt. %.

A reaction between isocyanate groups and amino groups may also occurduring the hydrolysis of the isocyanate group-containing trimerizationproducts. This results in heterocyclic polyamines with urea groupings asa byproduct of the hydrolysis. Such polyamines can also be used in theepoxy resin mixtures according to the invention as additive hardeningcomponents together with the actual hardening agent. In addition to theactual hardening agent or hardening mixture of the above-mentioned type,aromatic polyamines of another type, such as 4,4'-diaminodiphenylmethaneand 4,4'-diaminodiphenylsulphone, and/or other heterocyclic polyaminescan be used. The content of such polyamines in the hardening mixture isgenerally 30 wt. % maximum.

The equivalent ratio between the epoxy function and amine hydrogenfunction can be 1:0.5 to 1:1.1, and is preferably 1:0.7 to 1:0.9.

The epoxy resin mixtures according to the invention can also containaccelerators which, as is known, play an important role in the curing ofepoxy resins. Normally tertiary amines or imidazoles are used.Appropriate amines include, for example, tetramethylethylenediamine,dimethyloctylamine, dimethylaminoethanol, dimethylbenzylamine, 2,4,6-tris (dimethylaminomethyl )-phenol,N,N'-tetramethyldiaminodiphenylmethane, N,N'-dimethylpiperazine,N-methylmorpholine, N-methylpiperidine, N-ethylpyrrolidine,1,4-diazobicyclo (2,2,2)-octane, and chinolines. Appropriate imidazolesinclude, for example, 1-methylimidazole, 2-methylimidazole,1,2-dimethylimidazole, 1,2,4,5-tetramethylimidazole,2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, and1-(4,6-diamino-s-triazinyl-2-ethyl)-2-phenylimidazole. The acceleratoris used in a concentration of 0.01 to 2 wt. %, preferably 0.05 to 1 wt.%, always referred to the epoxy resin mixture.

The different components are dissolved separately or together ininexpensive solvents, such as acetone, methylethylketone, ethyl acetate,methoxyethanol, dimethylformamide, and toluene, or in mixtures of suchsolvents to prepare prepregs, the solutions can be combined in a singlesolution. The solution is then processed on conventional impregnationsystems, i.e., systems for soaking inorganic or organic materials suchas glass, metal, minerals, carbon, aramide, polyphenylene sulfide, andcellulose, as well as woven or non-woven fabrics made of such materials,or used for coating flat shaped articles such as metallic or plasticfilms. The impregnation solutions may also contain other halogen-freesubstances to improve the flame-resistance, which may be applied in ahomogenous solution or as a dispersed system. Such additives caninclude, for example, melamine cyanurates, melamine phosphates,pulverized polyetherimide, polyethersulfone, and polyimide.

Glass fiber fabrics are predominantly used for the manufacture ofprepregs for circuit board technology. In particular prepregs made ofglass fiber fabric types with a surface density of 25 to 200 g/m² areused for multilayer circuit boards. With impregnation solutions of theaforementioned type, prepregs with low surface densities can also beproduced as needed. The impregnated or coated reinforcing materials orembedding components are dried at a high temperature, which removes thesolvent and causes pre-polymerization of the impregnation resin.Overall, an extraordinarily favorable cost-to-feature ratio can beobtained in this manner.

The coatings and prepregs obtained are non-tacky and have a shelf-lifeof three months or longer at room temperatures, i.e., have sufficientshelf life. They can be pressed at temperatures up to 220° C. to formcomposites, which have high glass transition temperatures (≧180° C.) andinherent flame-resistance. If glass fiber fabrics in a proportion of 60to 62 wt. % referred to the laminate are used as the embedding material,the burning test according to UL 94 V can be safely passed with a V-0classification without adding halogen compounds or other flame-retardantadditives, even with test specimens with wall thicknesses as low as 1.6or even 0.8 mm. It is especially advantageous that no corrosive orparticularly toxic cleavage products are formed and smoke development isconsiderably less than for other polymeric materials, particularlybromine-containing epoxy resin molded materials.

The cured composites are also distinguished by their small thermalexpansion coefficients that remain constant over a broad temperaturerange and high chemical resistance, corrosion resistance, low waterabsorption, and excellent electrical properties. Adhesion to thereinforcing and bonding materials is outstanding. When using reinforcingmaterials of the above-mentioned type, prepregs for constructionmaterials supporting high mechanical stresses are obtained. Theseconstruction materials are suitable, for example, for applications inmachine construction, vehicle manufacturing, aerospace industry, andelectrical engineering, in particular in the form of prepregs forcircuit board manufacturing, specifically for manufacturing multilayercircuits.

Especially advantageous for use as circuit board material is the highadhesion strength of copper circuit paths, as well as the highdelamination resistance. Using the epoxy resin mixtures according to theinvention, materials, in particular multilayer circuit boards, aremanufactured, where thin cores of less than/equal to 100 μm havingsufficient solder bath resistance even for IR soldering processes areused.

The invention is further explained using the embodiments (MT=parts byweight).

EXAMPLES 1 THROUGH 3 Manufacturing of prepregs

A solution of A MT of a phosphorus-modified epoxy resin (P/EP resin) inthe form of a reaction product (epoxy value: 0.35 mol/100 g; phosphoruscontent: 3.4%) of an epoxidized novolak (epoxy value: 0.56 mol/100 g;average functionality: 3.6) and propanephosphonic acid anhydride in E MTmethyl-ethyl ketone (MEK), F MT dimethylformamide (DMF) and G MT ethylacetate (EA) is mixed with B MT of a polyamine obtained by trimerizationof a 4:1 mixture of toluene-2,4-diisocyanate andtoluene-2-6-diisocyanate and subsequent hydrolysis (to a product with anNH₂ value of 9.35%), C MT of a phenoxy resin with a molecular weight of30,000 and a hydroxy value of 6% (phenol resin), and D MT2-methyl-imidazole (MeIm). With the resin solution thus obtained, glassfiber fabric specimens (fabric type 7628, surface density 197 g/m²) werecontinuously impregnated using a laboratory impregnation system, anddried in a vertical drier at temperatures from 50° to 160° C. Theprepregs thus obtained are non-tacky and stable in storage at roomtemperature (max. 21° C. and max. 50% relative humidity). Thecomposition of the impregnation resin solutions and the properties ofthe prepregs are summarized in Table 1.

Example 4 Comparative test

The procedure of examples 1 through 3 was followed, however, withoutadding phenoxy resin (C). The resin solution obtained was processed asin Examples 1 through 3. The composition of the impregnation resinsolution and the properties of the prepregs are summarized in Table 1.

                  TABLE 1                                                         ______________________________________                                        Composition of the impregnation resin solutions and the                       properties of the prepregs                                                    Example #                                                                     Components (MT) 1      2         3    4                                       ______________________________________                                        A (P/EP resin)  160    160       160  160                                     B (Polyamine)   33     33        33   33                                      C (Phen. Resin) 10     7         6    --                                      D (MeIm)        0.4    0.4       0.4  0.4                                     E (MEK)         100    100       100  100                                     F (DMF)         50     50        50   50                                      g (EA)          10     10        10   10                                      Measured Values                                                               Residual Content:                                                             Solvent (%)     0.1    0.2       0.2  0.1                                     Residual gel time of the                                                                      140    117       125  120                                     prepregs at 170° C. (s)                                                ______________________________________                                    

The residual gel time is determined by applying the glass fiber-freeimpregnation resin (0.2 to 0.3 g) mechanically removed from the prepregsonto a heating plate preheated to 170° C. After approximately 30 s, themelted resin specimen is evenly stirred with a glass or wooden rod. Thechange in viscosity is observed by drawing an approximately 50 mm longstring from the melt. Gelation has occurred when no more strings can bedrawn. The time period (in s) measured by a stopwatch) from the timewhen the resin is applied onto the heating plate until the prematurerupture of the string is the gel time.

Examples 5 through 8 Preparation and testing of the laminates

Prepregs prepared as in Examples 1 through 4 (glass fiber fabric type7628, surface density 197 g/cm²) were pressed into 1.5 to 1.6 mm thicklaminates consisting of eight layers of prepregs, laminated between two35 μm Cu foils (press parameters: 175° C., 30 to 35 bar, 40 min.);subsequently the laminate was post-cured for 2 h at 190° C. The glasstransition temperature T_(G) of the laminates was determined using DMTA(dynamic-mechanical analysis); average burning time was determinedaccording to UL 94 V, adhesion of the copper foil was determined, andthe Measling test, the high-pressure cooker test, and the solder bathresistance test were performed. The values obtained are summarized inTable 2.

                  TABLE 2                                                         ______________________________________                                        Properties of the laminates                                                   Properties of the                                                             Laminates                                                                     ______________________________________                                        Example #       5      6         7    8                                       Prepregs corresponding                                                                        1      2         3    4                                       to Example #                                                                  Measured Values                                                               T.sub.G (°C.)                                                                          184    187       186  190                                     Average burning time                                                                          4.6    4.0       4.1  3.5                                     according to UL 94 V (s)                                                      Classification  V-0    V-0       V-0  V-0                                     Adhesion of the Cu foil                                                                       2.2    2.2       2.0  1.7                                     in the RT (N/mm)                                                              Measling Test (LT26)                                                                          +      +         +    +                                       High-Pressure Cooker                                                                          >20    >20       >20  >20                                     Test (s)                                                                      Solder Bath Resistance                                                                        140    174       180  100                                     at 288° C. (s)                                                         ______________________________________                                    

The tests were performed on the laminates in the following manner:

Adhesion capacity of the copper lamination

A 25 mm wide and 100 mm long strip of the copper foil was removed fromthe glass-reinforced laminate over a length of 20 mm and torn offperpendicularly with a suitable device at a tear-off rate of 50 mm/min;the force F (N) required was measured.

Measling test

The test was performed on specimens without copper lamination (size: 20mm×100 mm). The specimens were dipped into a 65° C. LT26 solution for 3min. (composition: 850 ml de-ionized H₂ O, 50 ml HCl p.a., 100 g SnCl₂.2H₂ O, 50 g thio-urea), rinsed with running water and subsequentlyplaced in boiling water for 20 min. After air drying (2 to 3 min), thespecimen was dipped into a 260° C. solder bath for 10 s. The laminateshould not delaminate.

High-pressure cooker test

Two specimens 50 mm×50 mm were placed into a steam atmosphere at atemperature of 120° to 125° C. in a high-pressure autoclave for 2 h.Subsequently the dried specimens were placed on a 260° C. hot solderbath within 2 min. for 20 s. The specimens should not delaminate.

Solder bath resistance

The test was performed according to DIN IEC 259 using a solder bathaccording to section 3.7.2.3. 25 mm×100 mm specimens were dipped into asolder bath at 288° C., and the time to the appearance of delaminationor bubbles was measured.

What is claimed is:
 1. An epoxy resin mixture for the production ofprepregs and composites, comprising:a phosphorus-modified epoxy resinwith an epoxy value of 0.02 to 1 mol/100 g, made up of structural unitsderived from (a) polyepoxy compounds with at least two epoxy groups permolecule and (b) phosphinic acid anhydrides, phosphonic acid anhydrides,or phosphonic acid half-esters; a glycidyl group-free compound withphenolic OH groups in the form of bisphenol-A, bisphenol-F, or a phenoxyresin obtained through the condensation of bisphenol-A or bisphenol-Fwith epichlorohydrin; an aromatic polyamine of the following structureused as a hardening agent: ##STR2## where one of the radicals R¹ and R²on each aromatic partial structure denotes a H atom and the other onedenotes an alkyl group.
 2. Epoxy resin mixture according to claim 1,wherein the phosphorus content of the epoxy resin mixture is 0.5 to 5wt. %.
 3. Epoxy resin mixture according to claim 2, wherein thephosphorus content of the epoxy resin mixture is 1 to 4 wt. %.
 4. Epoxyresin mixture according to claim 1, wherein the phosphorus content ofthe phosphorus-modified epoxy resin is 0.5 to 13 wt. %.
 5. Epoxy resinmixture according to claim 4, wherein the phosphorus content of thephosphorus-modified epoxy resin is 1 to 8 wt. %.
 6. Epoxy resin mixtureaccording to claim 1, wherein the proportion of the glycidyl group-freecompound in the resin mixture is up to 20 wt. %.
 7. Epoxy resin mixtureaccording to claim 6, wherein the proportion of the glycidyl group-freecompound in the resin mixture is up to 10 wt. %.
 8. Epoxy resin mixtureaccording to claim 1, wherein the ratio between epoxy function and aminehydrogen function is 1:0.5 to 1:1.1.
 9. Epoxy resin mixture according toclaim 8, wherein the ratio between epoxy function and amine hydrogenfunction is 1:0.7 to 1:0.9.
 10. Epoxy resin mixture according to claim1, wherein the hardening agent content in the resin mixture is 1 to 45wt. %.
 11. Epoxy resin mixture according to claim 10, wherein thehardening agent content in the resin mixture is 5 to 30 wt. %.
 12. Epoxyresin mixture according to claim 1, wherein the hardening agent ispresent together with other aromatic and/or heterocyclic polyamines. 13.Epoxy resin mixture according to claim 1, wherein it contains a curingaccelerator.
 14. Epoxy resin mixture according to claim 13, wherein thecuring accelerator is a tertiary amine or an imidazole.
 15. A circuitboard made of prepregs manufactured from glass fiber fabrics and theepoxy resin mixture according to claim 1.